A gas turbine engine typically includes a fan section, a compressor section, a combustor section and a turbine section. Air entering the compressor section is compressed and delivered into the combustion section where it is mixed with fuel and ignited to generate a high-speed exhaust gas flow. The high-speed exhaust gas flow expands through the turbine section to drive the compressor and the fan section. The compressor section typically includes low and high pressure compressors, and the turbine section includes low and high pressure turbines.
Gas turbine engines are removed from service and each part including compressor and turbine rotors are inspected for defects including cracks. Crack propagation rates for specific rotor materials, temperature and loading characteristics limit the life of a rotor. Once parts reach a determined limit, they are scrapped. Compressor and turbine rotors are costly parts and therefore any additional use or extension of life provides substantial value.